=>((a|b|\p{Nd}){1,2}|aaa|bbbb){1,2}

bab

aaca

aaabbbb

a0b

aa0aaa

b0aaa

=>(\d{1,3}\.){3}\d{1,3}

1.2.3.4

1.22.333.44

1.2.3

1..2.3